Deoxyribonucleic Acid (DNA) and Its Structure

The modern understanding of DNA has developed significantly over time, starting with the discovery of nucleic acid. In 1869, Friedrich Miescher conducted experiments using white blood cells, which he obtained from pus collected on bandages at a local hospital. He used a salt solution to wash the pus off the bandages and then added a weak alkaline solution to the cells. This caused the cells to break open (lyse) and release their nuclei, which separated from the rest of the solution.

From these cell nuclei, Miescher extracted a unique chemical substance, which he named nuclein. He found that nuclein had a high phosphorus content and exhibited acidic properties. This led to the substance being called nucleic acid. By the early 1900s, scientists discovered that Miescher's nuclein was actually a mixture of proteins and nucleic acids. Later, it was understood that there are two types of nucleic acids:

1. DNA (deoxyribonucleic acid): Responsible for storing genetic information.
2. RNA (ribonucleic acid): It plays a crucial role in protein synthesis and other cellular processes.

This discovery laid the foundation for understanding the structure and function of DNA.

DNA is the main component of chromosomes and was discovered by Swiss biochemist Frederick Miescher in 1869 while studying white blood cells. Initially, it was thought to exist only in the nucleus of cells, so it was named nucleic acid. However, it was later found in other parts of the cell as well. DNA molecules are present in all living organisms, from viruses and bacteria to humans. They control the cell's functioning, growth, and reproduction, earning the title 'Master Molecules.'

DNA (Watson and Crick’s Model)

The structure of DNA is the same in all organisms. In 1953, Watson and Crick proposed a model of DNA's structure, describing it as two parallel strands of nucleotides coiled around each other in a double helix shape. This structure can be compared to a flexible, coiled ladder:

• The rails (sides) of the ladder are made of alternating molecules of sugar and phosphoric acid.
• The rungs (steps) of the ladder are pairs of nitrogenous bases held together by hydrogen bonds.

Each strand of DNA is made up of smaller units called nucleotides, which consist of

1. A nitrogenous base
2. A sugar molecule
3. A phosphoric acid molecule

There are four types of nitrogenous bases

• Adenine (A) and Guanine (G) are called purines (double-ringed structures)
• Cytosine (C) and Thymine (T) are called pyrimidines (single-ringed structures)

The two strands of DNA are linked by hydrogen bonds between nitrogenous bases, forming specific base pairs

• Adenine (A) always pairs with Thymine (T)
• Cytosine (C) always pairs with Guanine (G)

This unique pairing ensures the DNA molecule's stability and allows it to carry genetic information. The alternating sugar and phosphoric acid molecules form the backbone, while the nitrogenous bases form the rungs, creating the ladder-like structure of the DNA molecule.

DNA Structure

A gene is a specific segment of a DNA molecule found on a chromosome. Each chromosome is made up of a single DNA molecule, and these genes are arranged in a linear sequence along the DNA strand. The variety in the sequence of nucleotides in DNA results in the formation of different types of genes.

• Genes play a crucial role in controlling the structure and function of cells and the body. They are responsible for passing hereditary characteristics from parents to their offspring; that is why there are many similarities between parents and their children. For this reason, genes are known as the functional units of heredity.
• Genes also store important information needed for protein synthesis, which is essential for the functioning and development of an organism.

• In 1990, the Human Genome Project was launched as a global effort by scientists to decode the complete DNA sequence of the human genome.
• In June 2000, the scientists involved in this project, along with Celera Genomics Corporation (a private company in the USA), announced the successful discovery of the entire human genome sequence.
• From this research, scientists determined that the human genome contains approximately 20,000 to 30,000 genes. Following this breakthrough, the genomic sequences of many microorganisms were also discovered. This progress in genomics has been highly beneficial in the field of medicine.
• By identifying disease-causing genes, it is now possible to diagnose and treat genetic diseases more effectively. This research has paved the way for advancements in understanding, preventing, and curing many genetic disorders.